A conventional circuit board for use in a keyboard is shown in FIGS. 6 and 7, where the board is indicated by reference numeral 28. This board 28 consists of a first pattern sheet 25, a second pattern sheet 26, and an insulating sheet 27 sandwiched between the pattern sheets 25 and 26. Each of the pattern sheets is made from a flexible insulating material and has a circuit pattern arranged thereon such that the circuit patterns on the two sheets 25 and 26 are opposed to each other. The insulating sheet 27 is provided with a hole. When the circuit board 28 and electrical parts 30 such as rheostats are mounted, the board 28 is joined to a support base 29, while the terminals 33 of the electrical parts 30 are inserted into holes 32 formed in a printed circuit board 31 that is provided independent of the circuit board 28. The terminals 33 of the parts 30 are connected with the circuits of the printed circuit board 31 as by soldering. The circuit board 28 has edge connectors 22c and 22d for making connections to other circuits. Also, the printed circuit board 31 on which the electrical parts 30 are mounted has an edge connector 34 for making connections with other circuits.
However, the edge connectors for making connections to an external circuit and an insulating circuit board having resistors, for example, thereon are indispensable to the electrical parts such as rheostats. Further, the electrical parts are required to be mounted above the surface of the printed circuit board in a spaced relation from the surface to prevent flux from flowing into the electrical parts when the parts are soldered to the printed circuit board. For these reasons, such a problem arises that the assembly of the printed circuit board and the electrical parts has a large height. Therefore, in spite of the fact that the circuit board forming a portion of a control panel is thin, the whole control panel occupies a considerable portion of the volume of the electrical product. This makes it difficult to manufacture the product in small size and small thickness. Another problem with the prior art structure is that the printed circuit board on which electrical parts are mounted and the edge connectors formed on the printed circuit board are necessary. Further, soldering operations are needed to make connections with these portions. Hence, the product is expensive to fabricate